During the last few years, epidural opioid drugs have been used in some centres instead of local anaesthetics. Epidural opioids behave quite differently from local anaesthetics and do not interrupt, or "block", nerve transmission. Accordingly, they do not cause muscle weakness or interfere with sensation other than pain. Unfortunately, while epidural opioids are very effective in relieving postoperative pain, most studies have found them to be inadequate by themselves during labour. When combined with local anaesthetic, however, they are much more reliable. Moreover, the addition of an opioid permits further reductions in local anaesthetic dosages to occur. Consequently, the incidence and severity of local anaesthetic side effects are also reduced. For these reasons, low-dose epidural local anaesthetic-opioid mixtures are becoming more and more popular.